This invention relates generally to a gear arrangement for transmitting torque and to a method of doing the same. More specifically, the present invention provides a gearing system for evenly distributing a torque between three gears and to a method of operating such system, as well as to a method of driving an output gear.
A variety of gear arrangements have been used for transmitting torque through an angle. A spur gear driving a face gear is one such arrangement. A spur gear is a wheel with straight gear teeth on its circumference, the teeth edges being parallel to the axis of the rotation. A face gear is a gear wheel having its axis of rotation at an angle to that of the driving spur gear. The teeth on the face gear are located on the end face of the wheel, with the teeth edges directed toward the axis of the rotation. The spur gear can move freely along its axis of rotation, within the limits of the length of its teeth. Furthermore, a spur gear has more tolerance for movement toward or away from a driven face gear than does an equivalent spiral bevel gear. A spur gear/face gear combination (i.e., a spur gear meshed with a face gear) optimizes the torque transfer capability between such gears as the speed reduction ratio increases.
Bevel gears also are used to transmit torque through an angle. Spiral bevel gears have curved teeth that carry more load than straight bevel gears. However, spiral bevel gears are very sensitive to changes in relative location. Thermal growth and deflections under load are serious limitations to spiral bevel gears. Therefore, spiral bevel gears are best suited to low speed reduction ratios close to 1 to 1. In addition, spiral bevel gears do not have conjugate action, resulting in minute acceleration and deceleration of the driven gear. The speed changes manifest themselves as noise and vibration.
Torque splitting has been attempted in transmissions. The reduced torque in parallel paths results in smaller and lighter components and smaller and lighter gearboxes. Various arrangements have been proposed. However, one problem has been an automatic precise torque split. A further problem is to reduce the number of stages needed between the input and output speeds. The way to reduce the number of stages is to increase the reduction ratio per stage.